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Humid media transfer device and/or printing media transfer device of printing machinesRelated Patent Categories: Printing, Printing Members, Rolling Contact, Yielding SurfaceHumid media transfer device and/or printing media transfer device of printing machines description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060185541, Humid media transfer device and/or printing media transfer device of printing machines. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The invention relates to a roller or a rubber blanket for a printing press, with a covering made of an elastomeric material with an outer surface as a damping solution and/or printing agent transfer device for printing presses for indirect or direct transfer of a damping solution and/or printing agent to a print carrier, and use of a roller or rubber blanket of this kind, and a printing press with a roller or rubber blanket of this kind (also generally referred to as a printing blanket). [0002] Rollers or rubber blankets of this kind for printing presses are used in offset printing, for example. In this context, the printing agent, e.g. a customary printing ink, is transferred from a reservoir, via an inking unit to a printing plate, to which the respective image is applied, generally by a photomechanical process. The printing areas of the printing plate accept the ink, such that the image to be printed can be transferred to a rubber blanket that is likewise mounted on a cylinder. The printing ink is transferred from the rubber blanket to the respective print carrier, i.e. the material to be printed, such as a paper web, a film, or some other object. At the same time, the printing plate is wetted with a damping solution, which is supplied from a reservoir by a damping unit. The damping solution covers the non-printing areas of the printing plate, such that they do not accept ink, thereby producing the print image. The damping solution is usually water, which can contain alcohols or other additives. In this context, the damping unit and the inking unit each consist of a plurality of rollers, where, in some cases, rollers with an elastomeric covering work against rollers with a metallic, ceramic or plastic surface in order to homogenize the printing agent and the damping solution in the gap between the rollers (nip), prepare them in a uniform layer and ultimately apply them to the printing plate and the rubber blanket. [0003] The rollers with an elastomeric covering have to satisfy a host of requirements, particularly demonstrating defined mechanical properties, such as hardness, wettability with the printing agent or the damping solution, mechanical and chemical resistance, abrasion resistance, good cleanability and the like. [0004] Moreover, particular problems are posed by defined transfer of ink and damping solution from the respective ink and damping solution reservoir, via the respective inking and damping unit to the impression cylinder. For example, it has become apparent that there is occasionally no defined transfer of damping solution and/or printing agent to the impression cylinder, and thus ultimately to the blanket cylinder, this being referred to as "overemulsification" of the ink/damping solution emulsion, i.e. too much damping solution, particularly water, is incorporated into the printing agent. The consequence of this is that, on both the impression cylinder and the rubber blanket, the areas covered with ink and the areas covered with damping solution are ultimately not accurately separated from each other, and thus that unsharp contours, streaks, or other such phenomena impairing the print quality, occur on the printed print carrier, e.g. a paper web. This "overemulsification" is partly attributed to fluctuating process conditions during the printing process, also including climate or temperature fluctuations in the print unit, for example, although these are difficult to determine and reproduce in terms of their process parameters. There is consequently a need to improve the print quality and enable a printing result that remains very constant over time. [0005] Furthermore, known rollers variously display disadvantages in terms of their back-transfer properties, i.e. the printing agent is not optimally transferred to the next roller in the nip, but carried back on the roller. This ultimately leads to undesirable distribution of the ink and can also result in undesirable transfer of ink into the damping unit. Moreover, in the event of a color change, some of the original ink can be taken up by the roller or the rubber blanket and transferred to the subsequent print unit, this possibly leading to undesirable color deviations. These problems have likewise not yet been satisfactorily resolved. An additional aim is to further improve the back-transfer properties of the rollers. [0006] Moreover, starting from rollers with auxiliaries, such as fluorinated polyolefins, incorporated in the elastomeric roller covering, it is desirable to further improve the long-term stability of the roller, and thus the service life of the printing press and the maintenance effort involved. [0007] Furthermore, consideration must be given to the fact that rollers and rubber blankets with an elastomeric covering are subject to wear in printing presses, this leading to a change in the surface properties of the roller or the rubber blanket, e.g. to a roughness that changes in the course of long periods of time, and changing wetting properties in relation to the printing agent and the damping solution. As a result, it becomes necessary to replace the roller covering and fit the roller core with a new covering at certain intervals. This leads to machine downtimes and is also cost-intensive, since the covering has to be removed entirely and a complete, new roller covering built up. [0008] The object of the invention is therefore to provide a damping solution and/or printing agent transfer device in the form of a roller or a rubber blanket for printing presses that solves the problems described above, particularly enables a virtually optimum printing result over long periods of time, even in the event of changing process conditions, such as climate or temperature fluctuations, particularly also in terms of color quality in multicolor printing, that demonstrates excellent back-transfer properties, displays a substantially longer service life with unchanged properties, particularly as regards hardness and wettability with damping solution and/or printing agent, and that permits simple restoration in the event of wear induced by operation. [0009] According to the invention, a roller or a rubber blanket is provided as a damping solution and/or printing agent transfer device that displays a continuous surface coating covering the covering of elastomeric material, said coating containing or entirely consisting of a fluoroelastomer, and where the surface coating preferably displays a layer thickness less than/equal to 100 .mu.m and/or a roughness Ra less than/equal to 1 .mu.m. The fluoroelastomer can be one or more elastomers selected from the group comprising elastomeric fluorinated rubber, polyfluoroalkoxyphosphazene and polyfluorosilicone. In particular, when used below, the term fluoroelastomer is in each case always to be understood as also explicitly meaning an elastomeric fluorinated rubber, this constituting a particularly preferred embodiment of a fluoroelastomer. [0010] In contrast to Teflon-coated rollers, for example, the fluoroelastomer according to the invention provides a surface coating that consists of an elastomeric material, like the covering bearing the coating itself. This constitutes the special adaptation of the roller coating to the covering made of elastomeric material, for which purpose Teflon coatings, such as PTFE, Teflon FEP.RTM. (tetrafluoroethylene hexafluoropropylene copolymer) or other coatings made of non-elastomeric or plastically deformable polymers, such as polyvinylidene fluoride and the like, would be totally unsuitable, such that the roller surface has a high dynamic load-bearing capacity, this being of major importance both for processing of the printing agent in the nip between two rollers working against each other and also in the case of rubber blankets. The comparatively thin surface coating thus has virtually no impact on the elastic and/or dynamic properties of the covering. [0011] It has furthermore been established that use of fluoroelastomer coatings of this kind in accordance with the invention, particularly of a fluorinated rubber, is capable of achieving highly defined and constantly consistent transport of the printing agent or the damping solution, such that overemulsification of the printing agent with damping solution, which impairs the printing quality, can be reliably avoided, even under a wide range of different process conditions. This makes it possible to improve the printing quality and, in particular, also avoid disruptive influences on the printed result, caused by changes in external conditions or process parameters. The printing process can thus be performed with greater process stability, e.g. also in the event of fluctuating external conditions, such as temperature fluctuations, and yields a constantly optimum printing result over long periods of time, with exact transitions between printing and non-printing areas. This is further promoted by the fact that rollers or rubber blankets according to the invention display virtually no tendency towards superficial accumulation of hydrophilizing substances from detergents, of pigments or calcium complexes from paper coatings or ink, or the like. These advantages particularly also exist compared to rollers with only fluorinated polyolefins incorporated in the elastomer covering, and the base elastomer of the covering forming part of the roller surface. Rollers of this kind would not solve the problems on which the invention is based. [0012] Furthermore, rollers according to the invention demonstrate outstanding back-transfer properties, substantially exceeding those of rollers in which, for example, fluorinated polyolefins are incorporated in an elastomeric covering and large proportions of the roller surface are thus provided by the base elastomer. In this context, the surface coating according to the invention ensures that a damping roller transfers virtually no printing agent, e.g. ink, back into the damping unit and, on the other hand, a coated ink roller transfers virtually no water back into the inking unit, this resulting in overemulsification being avoided in both cases. Furthermore, in the case of ink rollers, the local ink reservoir in an inking unit is reduced, the ink turnover thus being accelerated. Furthermore, a rubber blanket according to the invention transfers no water back from the image-producing printing plate, this leading to lower water settings in the wet offset process and avoiding overemulsification, and, on the other hand, transfers no ink from the preceding print unit back from the freshly printed print carrier, this permitting far more accurate color control. Surprisingly, the surface coating according to the invention fulfils the specified requirements equally well, depending on the application. [0013] Furthermore, the rubber blanket according to the invention displays markedly reduced paper web deformation in the curling test (described, for example, as the curling and bulging test in DIN 6723 and DIN 6724). Thus, conventional rubber blankets generally display a bulge of 35 mm, or of 15 mm at best, whereas rubber blankets according to the invention can display a bulge of .ltoreq.10 mm, or easily also .ltoreq.8 or .ltoreq.5 mm (in each case for 50 sheets, solid density approx. 1.50 DV cyan). As a result, far more accurate color control is possible, and film doubling is reliably avoided. [0014] Furthermore, compared to conventional rubber blankets, the rubber blanket according to the invention achieves far better printing quality in multicolor printing in terms of ink feed and color control of the printing result. This is achieved by particularly high dot accuracy in printing agent transfer, this leading to high color accuracy of the printing result. This is of decisive importance in multicolor printing, in particular, since the dot accuracy of the screen-like transfer of the individual ink dots of different color is of eminent importance for the printing result. This is attributed to the special interaction of the print carrier with the rubber blanket, which surprisingly also yields particularly quiet running of the printing agent carrier, which additionally permits higher printing speeds. Without being bound by theory, it is assumed that this is attributable to the special physicochemical properties of the rubber blanket coating and its surface, such as the particularly low roughness, and the elastic properties of the cover layer, in which context the low thickness also results in the coating having virtually no influence on the deformation behavior of the covering, this being of essential importance. [0015] Furthermore, the coating made of a fluoroelastomer, particularly fluorinated rubber, provides a roller which displays a particularly long service life and, over its service life, virtually no changes in its properties, such as surface condition, wetting and swelling behavior vis-a-vis printing agent and/or damping solution, transfer of the printing agent and/or damping solution to downstream equipment of the printing press, such as a downstream roller or a rubber blanket, cleaning properties, etc. This is probably attributable to the fact that, under the process conditions, fluoroelastomers, particularly fluorinated rubbers, act as a diffusion barrier vis-a-vis a host of substances, such as solvents in the printing agents, plasticizers in the elastomeric coverings and the like. This simultaneously effectively prevents diffusion of solvent constituents from the printing agent into the roller, and also diffusion of plasticizers out of the roller over long periods of time, meaning that highly constant process control is possible. It goes without saying that the fluoroelastomer coating preferably contains no plasticizers. [0016] Furthermore, rollers and rubber blankets according to the invention are cleaned particularly easily, especially also of fast inks and inks containing metal pigments, such as used in offset printing, as a result of which downtimes are substantially reduced. In particular, this also results in very substantial savings on mineral oil-based cleaners, and the use of water-based cleaners becomes possible at all. [0017] The surface coating is preferably homogeneous over its depth profile, i.e. it displays no gradients as regards its physical properties, such as hardness, degree of crosslinking and/or its composition. The same can also apply to the elastomeric covering. [0018] The fluoroelastomer preferably completely covers the elastomeric covering, at least in the working area of the roller or the rubber blanket, preferably over the entire surface of the roller or the rubber blanket. The outer surface of the fluoroelastomer coating is preferably textureless and as smooth and level as possible, e.g. with an average roughness Ra pursuant to EN ISO 4287 or DIN 4768 of approx. .ltoreq.1 .mu.m, .ltoreq.0.4-0.5 .mu.m, .ltoreq.0.25 .mu.m or .ltoreq.0.1 .mu.m. [0019] The fluoroelastomer coating, and preferably also the elastomeric covering, is preferably virtually or completely free of pores. The fluoroelastomer coating preferably constitutes the outermost surface of the roller or the rubber blanket, coming into contact with the printing agent, although a further coating layer can, where appropriate, also be provided in the manner of a cover layer. Where appropriate, intermediate layers can be provided between the fluoroelastomer coating and the elastomeric covering, although it is preferable for no further intermediate layer to be provided, apart from an adhesive or primer layer. [0020] If the roller coating containing the fluoroelastomer contains further particulate constituents, such as fillers and/or non-elastomeric polymers, the fluoroelastomer preferably provides a continuous matrix accommodating the other constituents, such that a continuous, three-dimensional network structure is formed from the fluoroelastomer, and the coating as a whole displays elastomeric properties over its radial and both its lateral or circumferential directions of extension. The coating is preferably free of particulate, including fibrous, fillers. [0021] It goes without saying that the elastomeric covering is applied to a stable roller core consisting, for example, of a metal or another dimensionally stable material. The elastomeric covering is preferably mounted directly on the roller core, apart from a layer of adhesive or primer, where appropriate, although intermediate layers can also be provided, where appropriate. In the case of a rubber blanket, the blanket is mostly only coated with an elastomeric covering on one side, in which context several fabric plies can also be provided. [0022] The fluoroelastomer, particularly the elastomeric fluorinated rubber, is preferably present in the surface coating with a content of .gtoreq.40-50% by weight, preferably .gtoreq.75 or .gtoreq.85 or .gtoreq.90 or 95% by weight, referred to 100 parts by weight of the coating. The surface coating can consist entirely of the fluoroelastomer, particularly the elastomeric fluorinated rubber. The indicated percentages of fluoroelastomer or fluorinated rubber can alternatively each refer to 100 parts by weight elastomer or polymer of the coating. [0023] The fluoropolymer or the fluorinated rubber is particularly preferably formed of a fluorinated rubber latex. Latices of this kind are advantageous because of their surface properties, in particular, especially as regards the prevention of overemulsification and the properties as a diffusion barrier vis-a-vis solvents, plasticizers and the like. Within the meaning of the invention, a latex is taken to mean a colloidal dispersion of a polymer in an aqueous medium. The latex or the polymer can be produced naturally or synthetically. The latex can be produced by emulsion polymerization of suitable monomers, or by dispersion of polymers in a dispersing agent. The dispersed particles can have a mean diameter of approx. 0.2 to approx. 1 nm or up to approx. 2 or 5-10 nm, e.g. approx. 0.5 nm, without limitation. The latex can contain additives, such as dispersing agents, etc. [0024] It has furthermore become apparent that fluoroelastomers, particularly fluorinated rubbers and especially those based on fluorinated latices, demonstrate a particularly low storage capacity in terms of the uptake and storage of the printing agent or components thereof and/or of damping solution components, such as alcohols and the like. Continue reading about Humid media transfer device and/or printing media transfer device of printing machines... Full patent description for Humid media transfer device and/or printing media transfer device of printing machines Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Humid media transfer device and/or printing media transfer device of printing machines patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. 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